1. Field of the Invention
The present invention relates to a thermal processing susceptor holding a semiconductor wafer or a glass substrate (hereinafter simply referred to as “substrate”) thermally processed by photoirradiation and a thermal processing apparatus comprising this thermal processing susceptor.
2. Description of the Background Art
In general, a thermal processing apparatus such as a lamp annealing apparatus using halogen lamps is employed in an ion activation step for an ion-implanted semiconductor wafer. This thermal processing apparatus heats (anneals) the semiconductor wafer to a temperature of about 1000° C. to 1100° C., for example, thereby activating ions implanted into the semiconductor wafer. The thermal processing apparatus increases the temperature of a substrate at a rate of about several 100 degrees per second through the energy of light emitted from the halogen lamps.
However, it has been proved that the profile of the ions implanted into the semiconductor wafer is rounded, i.e., the ions are thermally diffused when the thermal processing apparatus increasing the temperature of the substrate at the rate of about several 100 degrees per second is employed for activating the ions implanted into the semiconductor wafer. In this case, ions must disadvantageously be implanted into the surface of the semiconductor wafer beyond necessity since the ions are diffused also when the same are implanted in high concentration.
In order to solve the aforementioned problem, Japanese Patent Application Laying-Open Gazette No. 59-169125 (1984) or 63-166219 (1988), for example, proposes a technique of irradiating the surface of an ion-implanted semiconductor wafer with flashlight through a xenon flash lamp or the like thereby increasing the temperature of only the surface of the semiconductor wafer in an extremely short time of not more than several ms. When the semiconductor wafer is heated with a xenon flash lamp in an extremely short time, there is no sufficient time for diffusing the ions and hence only ion activation can be carried out without rounding the profile of the ions implanted into the semiconductor wafer.
A conventional thermal processing apparatus, not necessarily employing a photoirradiation heating system, generally performs thermal processing while holding a substrate with a susceptor having excellent heat resistance, as proposed in Japanese Patent Application Laying-Open Gazette No. 10-74705 (1998) or 2000-355766, for example.
A xenon flash lamp instantaneously applies light having extremely high energy to a semiconductor wafer, and hence the surface temperature of the semiconductor wafer is abruptly increased in an instant. If the energy of the applied light exceeds a certain threshold in this case, it follows that the semiconductor wafer is cracked in a high probability due to abrupt thermal expansion of the surface. In practice, therefore, the xenon flash lamp emits light at an energy level less than the aforementioned threshold with a certain degree of allowance (process margin).
When the thermal processing apparatus heats a wafer with flashlight emitted from the xenon flash lamp while holding the semiconductor wafer with the susceptor, however, the semiconductor wafer may be cracked also when the energy level of the flashlight is less than the aforementioned threshold. If an end of the wafer is in contact with a pocket edge or a positioning pin of the susceptor when the surface of the wafer is abruptly thermally expanded due to the instantaneously applied flashlight to convexly warp the semiconductor wafer, large stress is applied to the contact portion while the wafer has no temporal allowance for slidingly moving on the susceptor in order to relax such stress. Consequently, the semiconductor wafer is cracked by the stress upon instantaneous thermal expansion if the end thereof is in contact with something, also when the applied flashlight has an energy level less than the aforementioned threshold.